You have to decide where your budget is. I would buy all lenses with IS if video is the first priority. The Sigma 17-50/2.8 OS is would be my first choice then the Tamron. Also on the wide side I have a Tokina 12-24, this a great lens, but the range of the Tamron 10-24 is far greater and more useful.
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Canon 7D / 50D (40D premature death. Long Live Canon)
CANON
70-200/2.8 - 135/2.0 - 100/2.0 - 85/1.8 - 35/2.0
SIGMA
EX 50-500 - EX 120-300/2.8 - 18-200OS - EX 18-50/2.8 II - EX 50/1.4
EX 10-20
TOKINA 12-24/4 (for sale1) - TAMRON 28-75/2.8, 17-50/2.8 - Samyang 8/3.5
KENKO Pro300 2XTC - 1.4XTC